Comparative Study on Corrosion Behavior and Mechanism of As-Cast Mg-Zn-Y and Mg-Zn-Gd Alloys

Rare earth (RE) elements have large solid solubility in magnesium and are widely used to regulate the microstructure and property of advanced magnesium alloys. However, different kinds of RE elements have different effects on microstructure and property of the alloy. In this study, a Mg-Zn-Y alloy and a Mg-Zn-Gd alloy with alloying elements of the same atomic percentage were designed to clarify the effect of yttrium (Y) and gadolinium (Gd) on the corrosion behavior of as-cast MgZn2Y2.66 and MgZn2Gd2.66 alloys. The results show that the MgZn2Y2.66 alloy is mainly composed of alpha-Mg phase and long period stacking ordered (LPSO) phase, while MgZn2Gd2.66 alloy is mainly composed of alpha-Mg phase and (Mg, Gd)(3)Zn phase (W phase). Generally speaking, the corrosion phenomena of the two alloys in 3.5 wt% NaCl solution are similar. In the early stages of exposure, the alloys underwent uniform corrosion at a relatively low corrosion rate. With prolonged exposure, localized corrosion became dominated and the corrosion rate was greatly increased. However, the corrosion rate of the MgZn(2)Y(2.66 )alloy, in terms of the corrosion current density, is about one order of magnitude lower than that of the MgZn2Gd2.66 alloy. The high corrosion resistance of the MgZn2Y2.66 alloy is mainly attributed to the presence of LPSO phase in form of continuous networks and the relatively high corrosion resistance of the corrosion product layer on the alloy.